The overall goal of this investigation is to develop an understanding of the ecological effects and potential environmental health hazards posed by chronic or acute PCB contamination of aquatic environments. Studies to be undertaken during the second year of the research project include: (1) The identification of PCB metabolites produced during in vitro and in situ bacterial degradation. (2) The assessment of the mutagenicity of bacterially produced PCB metabolites. (3) An evaluation of the toxicological impact of PCB contamination upon aquatic microorganisms; to include such response measurements as: respiration substrate turnover, heterotrophic potential, N2 fixation, nitrification and methanogenisis. (4) A comparative characterization of the bacterial isolates capable of PCB resistance or degradation and naturally occurring aquatic bacteria in the same aquatic environment. (5) An analysis of PCB biodegradation potential in a polluted aquatic environment.